Maryland Sen. Ben Cardin, the ranking member on the Senate Foreign Relations Committee, filed for re-election on Monday.

He will face four other Democrats, including Chelsea Manning, who was convicted of sharing military documents with WikiLeaks, as well as Jerome Segal, Richard Vaughn​​ and Debbie "Rica" Wilson.

Segal is​ a research scholar​​ ​at the Institute for Philosophy and Public Policy at the University of Maryland​,​​ Vaughn ​is a businessman and Wilson is a former public school teacher and college professor.

Cardin was a primary sponsor on the Countering Russian Influence in Europe and Eurasia Act of 2017, which ​was ​incorporated into a bill imposing sanctions on Russia and signed by President Trump in August, ​according to GovTrack.

The law included a Jan. 29 deadline to impose new sanctions, but the Trump administration let it pass.

The youngest elected speaker of the Maryland House of Delegates, Cardin served from 1979 to 1986. He then served in the U.S. House of Representatives from 1987 to 2007, representing Maryland's Third Congressional District. He was first elected in 1966 to the Maryland House of Delegates while still a University of Maryland law student.

In November, Cardin hosted a town hall in Lanham, where he addressed the latest tax reform bill, among other issues.

"Relief should go to middle-income families," he said in November. "We're losing the middle class in America and they're the ones who need the help."

He also addressed gun safety during the town hall.

"I don't know what more we can do before Congress takes action on gun safety legislation," Cardin said. "We see tragedies every week."

Laudan Nikoobakht, second from left, and three other friends jump over pictures of Chahar Shanbe Souri fire in the hallway at Stamp Student Union at the University of Maryland on Thursday, March 14, 2019 (Photo by Fatemeh Paryavi/For the Diamondback)